1. Field of the Invention
The present invention relates to a stator for an automotive alternator, and in particular, relates to a stator for an automotive alternator which is constructed by laminating steel plates.
2. Description of the Related Art
FIG. 6 is a cross section of a conventional automotive alternator, FIG. 7 is an overall perspective of a stator core in FIG. 6, and FIG. 8 is an overall perspective of a stator in FIG. 6.
This automotive alternator includes: a case 3 composed of an aluminum front bracket 1 and an aluminum rear bracket 2; a rotating shaft 6 disposed within the case 3 having a pulley 4 secured to a first end thereof; a Lundell-type rotor 7 secured to the rotating shaft 6; fans 5 secured to first and second axial end surfaces of the rotor 7; a stator 8 secured to an inner wall within the case 3; slip rings 9 secured to a second end of the rotating shaft 6 for supplying electric current to the rotor 7; a pair of brushes 10 sliding on surfaces of the slip rings 9; brush holders 11 accommodating the brushes 10; a rectifier 12 electrically connected to the stator 8 for converting alternating current generated in the stator 8 into direct current; and a regulator 18 fitted over the brush holder 11 for adjusting the magnitude of the alternating voltage generated in the stator 8.
Air intake openings 3a for sucking cooling air into the case 3 and air discharge openings 3b for expelling the cooling air to the outside by rotation of the fans 5 are formed in the case 3.
The rotor 7 includes a rotor coil 13 for generating magnetic flux by passing an electric current, and a pole core 14 disposed so as to cover the rotor coil 13, magnetic poles being formed in the pole core 14 by the magnetic flux. The pole core 14 is constituted by a first pole core body 21 and a second pole core body 22 which intermesh with each other. The first pole core body 21 and the second pole core body 22 are made of iron and include tapered first and second claw-shaped magnetic poles 23 and 24.
The stator 8 is constituted by a stator core 15 for passage of a rotating magnetic field from the rotor 7, and a stator coil 16 constructed by winding wires into the stator core 15, an output current flowing through the stator coil 16.
The above stator core 15 is constituted by a base portion 30 having notches 48 on an outer circumferential portion, and a plurality of tooth portions 31 which protrude radially inwards from the base portion 30. Slots 32 are formed between adjacent tooth portions 31, and wires are wound continuously into the slots 32.
FIG. 9 is a diagram showing the stator core 15 during manufacture. The stator core 15 is manufactured from a straight strip-shaped steel plate 35, which is stamped so as to have a frame portion 37 and a plurality of tooth segments 34 at an even pitch, by laminating and bending the steel plate 35 into a helical shape such that tips of the tooth segments 34 point towards a center. In this example, the stator core 15 is bent and formed by inserting shaping pins 36 into the slots 32. The laminated steel plate 35, which has a thickness of 0.5 mm, is integrated by laser welding at eight places on the outer circumferential portion.
In the automotive alternator described above, electric current is supplied from a battery (not shown) through the brushes 10 and the slip rings 9 to the rotor coil 13, generating magnetic flux. The claw-shaped magnetic poles 23 of the first pole core body 21 are magnetized with north-seeking (N) poles by this magnetic flux, and the claw-shaped magnetic poles 24 of the second pole core body 22 are magnetized with south-seeking (S) poles. At the same time, because the engine is driven by the pulley 4 and the rotor is rotated by the rotating shaft 6, a rotating magnetic field is applied to the stator core 15, generating electromotive force in the stator coil 16. This alternating electromotive force passes through the rectifier 12 and is converted into direct current, the magnitude of the current is adjusted by the regulator 18, and the battery is recharged.
As described above, the cooling air flow generated by the fans 5 is sucked in through the air intake openings 3a formed in the front-end and rear-end brackets 1 and 2, passing in close proximity to and cooling the rectifier 12 and the regulator 18 which are heat-generating portions at a rear end of the alternator, then passes from a radially inner side to a radially outer side between fan blades 5a at both the rear end and a front end, thereby cooling front-end coil ends 16a and rear-end coil ends 16b of the stator coil 16 before being expelled through the air discharge openings 3b. In other words, a high degree of heat is generated but the coil ends of the stator coil 16 whose output performance is affected by high temperatures are constructed so as to be reliably cooled by positioning them between the fan blades 5a and the air discharge openings 3b on the brackets 1 and 2.
In the automotive alternator of the above construction, the stator coil 16 has three phases, the rotor 7 has twelve magnetic poles, and the slots 32 are formed at a ratio of one per pole per phase, the total number of slots 32 being thirty-six.
Now, as disclosed in Japanese Patent Laid-Open No. HEI 4-26345, for example, a stator core is known which is formed with slots at a ratio of two per pole per phase with the aim of providing an automotive alternator in which output voltage is improved and voltage fluctuations are reduced by making an overlapping portion between the claw-shaped magnetic poles of the rotor and the tooth portions of the stator core as small as possible to reduce magnetic flux leakage through the tooth portions and reduce ripples in the rectified output voltage. For example, when the number of phases in the stator coil is three and the number of poles in the rotor is twelve, the total number of slots 41 in a stator core 40 is seventy-two, as shown in FIG. 10.
Because opening portions 42 of the slots 41 become narrow when the number of the slots 41 in the stator core 40 is seventy-two, it is difficult to continuously wind wires of a stator coil from a radially inner side of the stator core 40 through the opening portions 42.
A technical means for solving such difficulties is disclosed in Japanese Patent No. 2927288. FIG. 11 is a partial front elevation of a stator 44 in which a stator coil 43 has been mounted to the stator core 40 without difficulty using this technical means even though the number of the slots 41 in the stator core 40 is seventy-two.
This stator coil 43 is constituted by a plurality of electrical conductors 45, such as the one shown in FIG. 12. This electrical conductor 45 is constituted by first and second straight portions 46 and a turn portion 47 connecting the straight portions 46 to each other. The first straight portions 46 of the electrical conductors 45 are positioned on a radially inner side being on the opening portion 42 side in a radial direction of first slots 41 to form an inner layer, and the second straight portions 46 of the electrical conductors 45 are positioned on a radially outer side in a radial direction of second slots 41 to form an outer layer.
The electrical conductors 45 are inserted into the slots 41 from a first end surface of the stator core 40 and are stacked up on top of each other such that the turn portions 47 thereof line up in rows. The straight portions 46 on the inner layer and the outer layer which protrude at a second end surface of the slots 41 are bent in a circumferential direction of the stator core 40, and are connected in series to the straight portions 46 in a different layer of the electrical conductors 45 a distance of one pole away, forming the stator coil 43.
FIG. 13 is a partial perspective of an end surface of the stator 44 viewed from the end where the electrical conductors 45 are connected, and FIG. 14 is a partial perspective of the end surface of the stator 44 viewed from the end where the electrical conductors 45 are inserted.
In the automotive alternator constructed in this manner, because the opening portions 42 of the slots 41 become narrow when the number of slots per pole per phase is two, it is difficult to continuously wind wires of the stator coil from the radially inner side of the stator core 40 through the opening portions 42. As a means of solving this, as shown in FIGS. 15 to 17, the electrical conductors 45 are inserted from the first end surface of the slots 41 of the stator core 40, and after protruding from the second end surface of the slots 41, each of the straight portions 46 is bent (twist formation) in the circumferential direction of the stator core 40, and connected in series to the straight portions 46 of the electrical conductors 45 in a different layer a distance of one pole away.
In the conventional automotive alternator constructed in this manner, the stator coil generates heat due to the generated electric current and the temperature rises, causing a reduction in part life.
When the straight portions 46 are bent (twist formation) in the direction of arrows B, which is the circumferential direction, excessive stress is applied to core end portions, and one problem has been that on the radially inner side of the stator core 40 the steel plate 35 deforms circumferentially and misaligns as shown in FIG. 17, disturbing a magnetic circuit and reducing output voltage.
Another problem has been that when the electrical conductors 45 are inserted at the first end surface of the slots 41 of the stator core 40 in the direction of arrows C, tip end surfaces of the straight portions 46 come into contact with a peripheral edge portion of the slots 41 of the stator core 40, scraping the insulation coating off a surface of the electrical conductors 45 and causing poor pressure resistance.
Yet another problem has been that magnetic flux leakage arises at the tip surfaces of the tooth portions 31, decreasing output current.
The present invention aims to solve the above problems and an object of the present invention is to provide a stator for an automotive alternator which can suppress temperature increases, prevent drops in output, prevent poor pressure resistance, and prevent decreases in output current.
In order to achieve the above object, according to one aspect of the present invention, there is provided a stator for an automotive alternator, the automotive alternator including:
a rotor having first and second claw-shaped magnetic poles fitted onto a rotating shaft; and
a stator having a stator core supported between front-end and rear-end brackets, a stator coil which is connected into a three-phase alternating current connection being wound into the stator core,
the stator core including:
a core main body constructed by laminating a strip-shaped steel plate, the core main body including a base portion and a plurality of tooth portions protruding radially inwards from the base portion defining core main body slots; and
an end plate which is thicker than the steel plate being disposed on at least one end surface of the core main body.
The core main body may be constructed by laminating the strip-shaped steel plate formed with a plurality of tooth segments at an even pitch while bending the strip-shaped steel plate into a helical shape such that tips of the tooth segments point towards a center.
The core main body may be constructed by laminating a plurality of the steel plates in an axial direction, the steel plates being annular in shape and being formed with a plurality of tooth segments at an even pitch on an inner circumferential side.
Each of the tooth portions of the stator may be positioned to form an overlapping portion overlapping two of the first and second claw-shaped magnetic poles on the rotor facing the tooth portion, the two first and second claw-shaped magnetic poles having different polarity and being adjacent in a direction of rotation of the rotor, the end plate being disposed at one end of the overlapping portion thereof.
The rotor may have centrifugal fans on first and second axial end portions; and
coil ends of the stator core of the automotive alternator may be cooled by cooling air which is sucked in through air intake openings and expelled through air discharge openings disposed in the front-end and rear-end brackets.
The stator coil may be constructed by passing a plurality of generally U-shaped coil segments through the stator core from a first end of the stator core, then forming twists in the generally U-shaped coil segments at the end plate end, and joining together end portions of the generally U-shaped coil segments by welding, the generally U-shaped coil segments being made of copper having a generally flat cross-sectional shape having an insulation coating disposed thereon,
the stator coil including:
a pair of conductors disposed in a straight line in a radial direction in each of the core main body slots;
insulating paper for electrically insulating the coil segments from the stator core; and
a joint portion joining an inner-layer-side coil segment end and an outer-layer-side coil segment end.
A circumferential width dimension of an end plate slot formed in the end plate may be larger than a circumferential width dimension of the core main body slots formed in the core main body.
A corner portion at an end of the end plate slot formed on the end plate where the generally U-shaped coil segments enter may be eased.
A resin may be impregnated into a coil end, a greater amount of the resin being impregnated into the coil end at an end surface portion of the stator core than into other portions of the coil end.